# The Knotted Sky I: Planck constraints on the primordial power spectrum

## Abstract

Using the temperature data from Planck we search for departures from a power-law primordial power spectrum, employing Bayesian model-selection and posterior probabilities. We parametrize the spectrum with n knots located at arbitrary values of logk, with both linear and cubic splines. This formulation recovers both slow modulations and sharp transitions in the primordial spectrum. The power spectrum is well-fit by a featureless, power-law at wavenumbers k>10{sup -3} Mpc{sup -1}. A modulated primordial spectrum yields a better fit relative to ΛCDM at large scales, but there is no strong evidence for a departure from a power-law spectrum. Moreover, using simulated maps we show that a local feature at k ∼ 10{sup -3} Mpc{sup -1} can mimic the suppression of large-scale power. With multi-knot spectra we see only small changes in the posterior distributions for the other free parameters in the standard ΛCDM universe. Lastly, we investigate whether the hemispherical power asymmetry is explained by independent features in the primordial power spectrum in each ecliptic hemisphere, but find no significant differences between them.

- Authors:

- Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand)
- Department of Physics, University of California at Irvine, Irvine, CA 92697 (United States)

- Publication Date:

- OSTI Identifier:
- 22373375

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2014; Journal Issue: 08; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASYMMETRY; MAPS; MODULATION; SIMULATION; SKY; SPECTRA; UNIVERSE; YIELDS

### Citation Formats

```
Aslanyan, Grigor, Price, Layne C., Easther, Richard, and Abazajian, Kevork N., E-mail: g.aslanyan@auckland.ac.nz, E-mail: lpri691@aucklanduni.ac.nz, E-mail: kevork@uci.edu, E-mail: r.easther@auckland.ac.nz.
```*The Knotted Sky I: Planck constraints on the primordial power spectrum*. United States: N. p., 2014.
Web. doi:10.1088/1475-7516/2014/08/052.

```
Aslanyan, Grigor, Price, Layne C., Easther, Richard, & Abazajian, Kevork N., E-mail: g.aslanyan@auckland.ac.nz, E-mail: lpri691@aucklanduni.ac.nz, E-mail: kevork@uci.edu, E-mail: r.easther@auckland.ac.nz.
```*The Knotted Sky I: Planck constraints on the primordial power spectrum*. United States. doi:10.1088/1475-7516/2014/08/052.

```
Aslanyan, Grigor, Price, Layne C., Easther, Richard, and Abazajian, Kevork N., E-mail: g.aslanyan@auckland.ac.nz, E-mail: lpri691@aucklanduni.ac.nz, E-mail: kevork@uci.edu, E-mail: r.easther@auckland.ac.nz. Fri .
"The Knotted Sky I: Planck constraints on the primordial power spectrum". United States.
doi:10.1088/1475-7516/2014/08/052.
```

```
@article{osti_22373375,
```

title = {The Knotted Sky I: Planck constraints on the primordial power spectrum},

author = {Aslanyan, Grigor and Price, Layne C. and Easther, Richard and Abazajian, Kevork N., E-mail: g.aslanyan@auckland.ac.nz, E-mail: lpri691@aucklanduni.ac.nz, E-mail: kevork@uci.edu, E-mail: r.easther@auckland.ac.nz},

abstractNote = {Using the temperature data from Planck we search for departures from a power-law primordial power spectrum, employing Bayesian model-selection and posterior probabilities. We parametrize the spectrum with n knots located at arbitrary values of logk, with both linear and cubic splines. This formulation recovers both slow modulations and sharp transitions in the primordial spectrum. The power spectrum is well-fit by a featureless, power-law at wavenumbers k>10{sup -3} Mpc{sup -1}. A modulated primordial spectrum yields a better fit relative to ΛCDM at large scales, but there is no strong evidence for a departure from a power-law spectrum. Moreover, using simulated maps we show that a local feature at k ∼ 10{sup -3} Mpc{sup -1} can mimic the suppression of large-scale power. With multi-knot spectra we see only small changes in the posterior distributions for the other free parameters in the standard ΛCDM universe. Lastly, we investigate whether the hemispherical power asymmetry is explained by independent features in the primordial power spectrum in each ecliptic hemisphere, but find no significant differences between them.},

doi = {10.1088/1475-7516/2014/08/052},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 08,

volume = 2014,

place = {United States},

year = {Fri Aug 01 00:00:00 EDT 2014},

month = {Fri Aug 01 00:00:00 EDT 2014}

}